Field of the Invention
The present invention relates to a video processing apparatus, a video processing method, and a medium.
Description of the Related Art
In a conventional video processing system including an imaging apparatus capable of sequentially capturing images of a subject and a display apparatus capable of displaying a video, both of the imaging apparatus and the display apparatus perform gradation correction processing based on gamma correction. The gradation correction processing (i.e., gamma correction processing) performed by the imaging apparatus includes converting a luminance input code value of a captured video signal into an output code value corresponding to a gamma characteristic of the imaging apparatus (i.e., a camera gamma). The gradation correction processing (i.e., gamma correction processing) performed by the display apparatus includes converting a luminance input code value of a supplied video signal into a luminance value based on a gamma characteristic of the display apparatus (i.e., a display gamma). Thus, only a limited part of the brightness of a subject having a very wide dynamic range in the real world can be segmented. It is possible to realize a satisfactory display in a definite narrow dynamic range of a monitor unit of the display apparatus.
Further, as a gradation correction processing technique capable of securing a practical input dynamic range for the imaging apparatus, a conventional technique discussed in Japanese Patent Application Laid-Open No. 2002-223373 widens the input dynamic range by performing gamma correction processing including knee correction.
The above-mentioned gamma correction processing including the knee correction is determined by compressing the contrast in both a middle-luminance region and a high-luminance region while securing the practical input dynamic range. However, compressing the contrast in the middle-luminance and high-luminance regions can result in, for example, unnaturalness, in a gradation characteristic of the entire system including the imaging apparatus and the display apparatus because the contrast in the high-luminance region is relatively compressed compared to the low-luminance region. More specifically, a gradation characteristic of a video displayed by the display apparatus can result in luminance change reduced in the high-luminance region, compared to a gradation characteristic of a real subject. Thus, the video displayed by the display apparatus is unnatural in that natural gradation, color, and sharpness of the real subject cannot be reproduced.
Meanwhile, there is a conventional gradation correction processing technique applicable to the display apparatus, which is capable of compensating the compressed contrast in the high-luminance region by increasing the brightness of the high-luminance region. However, the video signal output from the imaging apparatus does not include gradation information about the middle-luminance and high-luminance regions. Thus, the gradation cannot be sufficiently restored by only the processing performed by the display apparatus. Further, since the display apparatus cannot obtain information about the gamma characteristic of the imaging apparatus, it is difficult for the display apparatus to reproduce the natural gradation, color, and sharpness of the real subject.